Gravure printing means a printing type that covers a concave plate formed by corroding a flat plate with ink and scratches extra ink by doctor blade. Ink used herein is referred to as gravure ink. Unlike general gravure ink using a solvent, rotogravure hot melt ink uses ink melted by heating. Therefore, the rotogravure ink is eco-friendly gravure ink that does not discharge volatile organic compound or hazardous air pollutants.
The gravure ink has been prevalently applied in a plastic package industry such as a plastic package for foods, medicine, forage, agricultural products, and household goods. In particular, the gravure ink has been mainly used for a food package, or the like. However, due to in order to the environmental harmfulness caused by a solvent used for ink, a change to an eco-friendly product has been requested. As an alternative capable of using merits of the gravure printing while overcoming the environmental harmfulness, the rotogravure hot melt ink has been suggested.
The hot melt ink is made of a colorant and a vehicle. As the vehicle, poly (ethyl vinyl acetate) based resin is generally used. Japanese Patent Laid-Open Publication No. 2000-072992 discloses hot melt ink that uses poly (ethyl vinyl acetate) based resin as a vehicle and controls viscosity and pigment dispersibility, or the like, using alcohol and wax. Generally, the poly (ethyl vinyl acetate) based resin having a softening point of 160 to 170° C. is used about 60 to 70%, the wax having a melting point of 80 to 90° C. is used about 10 to 20%, and the alcohol having a high boiling point such as stearyl alcohol is used about 20 to 30%. These vehicle mixtures may include a small amount of additives such as dispersant, antioxidant, ultraviolet absorbent, or the like. A ratio of the vehicle to the pigment including the additive is about 98:1 to 80:20. In particular, the wax and the alcohol in the composition are an important fact of determining the melting point of the hot melt ink. The wax and the alcohol having the high boiling point, which are used to control the melting velocity, serve to lower adhesion, which makes it difficult to increase color density of the hot melt ink using the poly (ethyl vinyl acetate) based resin as the vehicle.